Air conditioning system



April 18, 1939. w. L. McGRATH 2,154,858

AIR CONDITIONING SYSTEM Filed May 14, 1938 2 Sheets-Sheet l- Smaentor William L. No Gra Uh Gttorneg April 18, 1939. w. L MCGRAT H 2,154,858

AIR CONDITIONING SYSTEM Filed May 14, 1938 2 Sheets-Sheet 2 Fig.2

Zinnantor William McGrakh Gttomeg Patented Apr. 18, 1939 UNITED STATES AIR CONDITIONING SYSTEM William L. McGrath, St. Paul, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application May 14, 1938, Serial No. 208,089

12 Claims.

This invention relates to an air conditioning system and more particularly to a system for removing sensible and latent heat from a space in accordance with the requirements of the space.

In accordance with my invention, air is circulated over the evaporator coil of a refrigeration system and through the space or spaces to be conditioned. The evaporator coil temperature is controlled according to whether the temperature or the humidity of the space should be lowered in order to maintain satisfactory conditions in the space. In cases where the temperature of the space only is too high the temperature of the evaporator will be maintained at a higher value than is the case where dehumidification is required. It is well known that in order to dehumidify the air, more heat must be removed from the air than is the case where a reduction in temperature of the space is required since in order to dehumidify, sensible heat and also latent heat must be removed from the airand it is therefore advisable to maintain a lower evaporation temperature when dehumidification is required than where only a reduction in temperature is required. Under certain conditions however the temperature of the space may be so high or in other words, the sensible cooling load of the evaporator may be so great that the evaporator operating at the higher temperature is unable to reduce the temperature the required amount and in such cases even though the humidity of the space is at the desired value the evaporator may be operated at the lower temperature. In order to control the evaporator in this manner, I have provided a pair of controls til responsive to difierent suction pressures on'the suction side of the refrigeration system, one of these controls controlling the compressor upon an initial increase in temperature of the space to maintain a relatively high suction pressure in the evaporator, and the other suction pressure controller controlling the compressor to maintain a lower suction pressure and accordingly a lower coil temperature when the temperature in the space reaches an excessively high value or when the humidity in the space becomes excesslve.

It is therefore an object of my invention to provide a novel control system for the evaporator coil of a refrigeration system in order to control the coil temperature in accordance with the cooling requirements thereof.

Other objects will become apparent upon reference to the specification, claims, and appended drawings wherein like reference characters represent like parts in the two views and wherein:

Figure 1 is a schematic view of one form of system embodying my invention, and

Figure 2 is a modification of the system illustrated in Figure 1.

Referring more specifically to Figure 1, an air conditioning chamber is represented by the reference character Ill. Located within this chamber is the evaporator l l of a refrigeration system to be described. A heating coil l2 may be located in the chamber In and a fan [3 driven by means of a motor I4 is provided for drawing air over the coils II and I2 and discharging the air from an outlet l5 into the space l6 to be conditioned;

The. air entering the chamber l0 may be fresh or outside air or a mixture of fresh and return air and the supply of air to the chamber l0 may be controlled in any suitable manner.

The refrigeration system of which the evapo .rator ll forms a part also includes a compressor 26 driven by a motor 2i which is controlled in a manner to be hereinafter described. Compressed refrigerant is discharged from the compressor 20 and flows through a pipe 22 into a condenser 23 whence the refrigerant flows through a pipe 24 through an expansion valve 25 which may be of any 'suitable well known construction and into the evaporator M. 'The evaporated refrigerant then flows through a pipe 26 back to the inlet of the compressor 20. Connected to the suction side of the refrigeration system by means of a pipe 28 are suction pressure controllers 2t and 3B. These controllers'comprise bellows 3i and 32, respectively, and cooperating therewith are levers 33 and 3d pivoted at and 36 and biased by means of springs 3i and 3t into engagement with the upper portion of the bellows 3i and 32,respectively. Lever 33 carries a mercury switch 40, this switch including contacts M and 42 and a mercury element 33. Similarly the lever 34 of the controller 3i! carries a mercury switchlld, this switch including contacts 46, and mercury element 48. As the pressure on the suction side of the system drops, the bellows 3i and 32 contract and the levers 33 and 3t move downwardly under the action of the biasing springs 31 and 38. When the pressure has dropped to a low enough value the switches carried by the levers are tilted in the other direction thus interrupting the circuit through the respective contacts thereof. These'switches are set to open at different suction pressures, for example, the switch 40 may open when the suction pressure drops to 40 pounds, for example, and the switch may remain in the closed position until the suction pressure has dropped to 25 pounds, for example.

Mounted within the space being conditioned "is a temperature responsive device 50, This device may include a bellows 5| containing-a volatile fill whereupon the bellows expands or contracts in accordance with temperature variations in the space. Cooperating with the bellows Si is a lever 52 biased by means of a spring 53 into engagement with the upper portion of the bel-. lows and a mercury switch 54 is carried by the lever 52. This switch 54 includes three contacts 56, 51, and 58 and a mercury-element 59. It will be noted that the contacts 56, 51, and 58 are of different lengths and are so arranged that as the temperature in the space increases and the switch 54 begins to tilt in the opposite direction from that shown, the mercury element 59 will first bridge the contacts 56 and 58 but will not engage the. contact .51 at first because this contact does not ,extendinto'the tube as far as the other contacts. As the temperature in the space continues to rise however the tube will be tilted further in the other direction and after the temperature reaches a predetermined value, the mercury will also engage the contact 51 and all the contacts will be bridged by the mercury element 59.

Also mounted in the space I6 is a humidity responsive device 66 which may be of any well 26 known construction and is shown as comprising a humidity responsive element 6| which is anchored atits lower end to a suitable supporting structure and is connected at ltsupper end to a lever 62 pivoted at 63 and biased upwardly by means of a spring 64. An increase in humidity of the air surrounding the element 6| causes this element to expand causing the lever 62 to move upwardly under the influence under the spring 64. As the humidity in the space decreases, the

80 element 6| contracts and causes the lever 62 to move downwardly. Carried by the lever 62 is a mercury switch 66 including contacts 61, 68 and a mercury element 69. It will be apparent that as the humidity in the space reaches a predetermined value the switch 66 will be tilted to a position wherein the contacts 61 and 68 are bridged by the mercury element 69.

Line wires 15 and 16 are provided for supplying power to the motor 2| these line wires being connected to a suitable source of power (not shown). When the temperature in the space is at the desired value, the mercury switch 54 will be tilted to a position wherein none of the contacts thereof are bridged by themercury element. 'Upon an increase in temperature in the space however,

to an undesirable value, the contacts 56 and 58 will first be bridged by the mercury element 59. This causes the motor 2| to be energized through the following circuit: from the line wire 16 through conductor 18, terminals 56 and 58 of the switch 54, conductors 19,86, switch 46 of the suction pressure controller 29, conductors 8|, 82, the switch of the suction pressure controller 36, conductor 83, motor 2 I, and conductor 84 to the line wire 15. Operation of the motor 2| causes operation ofthe compressor 26 whereupon the temperature of the evaporator begins to decrease thus removing heat from the air being circulated thereover and through the space I6. It should be noted that both switches 46 and 45 of the suction pressure controllers are. connected in series with the motor 2| and the switch 54 of the temperature responsive device 56. Accordingly should the pressure on the suction side of the system drop to the setting of the controller 29, as, for example, 40 pounds, the

switch 46 will be moved to circuit breaking position whereupon the motor 2| will stop. Since the suction pressure is an indication of the evaporator temperature it will be seen that upon an initial call for cooling within the space, assuming the humidity therein to be at a desirable value,

the compressor 26 will be operated only long and often enough to maintain a predetermined evaporator temperature until the space temperature drops to the desired value. In this way the heat removed from the air will be largely sensible heat which is all that is required since there is no call for dehumidification. I

Assuming now that the above described circuit through the compressor motor 2| is completed by reason 01 a need for cooling within the space, and the humidity therein rises to an undesirable value, the mercury switch 66 will be tilted to a position wherein the contacts 61 and 68 are bridged by the mercury element 69. There will now be a circuit through the motor 2| which is independent of the switch 46, this circuit being as follows: from the line wire 16 through conductor 18, contacts 56 and 58 of the switch 54, conductors 19, 86, switch 66, conductors 81, 88,

82, switch 45, conductor 83 through the motor 2| and conductor 84 to the line wire 15. Switch 46 is now shunted out of the controlling circuit for the motor 2| and the motor will now operate to maintain a suction pressure corresponding to the setting of the controller 36, as, for example. a pressure of 25 pounds or in other words, a lower coil temperature at the evaporator II. By reason of this lower coil temperature a large part of the heat removed from the air will be latent heat thus affecting a reduction of humidity in the space I6. The compressor 26 will now operate to maintain this lowered coil temperature as long as the humidity is excessive and the temperature is high enough so that contacts 56 and 58 of the switch 54 are connected.

Assuming now that the humidity in the space is at a desired value but the temperature continues to increase until all of the contacts in the switch 54 are bridged by the mercury element 59. Since there is now an increased demand for cooling within the space it may be desirable to maintain a lower evaporator temperature even though there is no need for dehumidification. The movement of the switch 54 to this new position closes a circuit to the motor 2| which shunts out the switch 46, this circuit being as follows: from the line wire 16 through conductor 18, contacts 56 and.51 of the switch 54, conductors 96, 88, 82, switch 45, conductor 83, motor 2|, and conductor 84 to the line wire 15. It will thus be seen that when the space temperature reaches an excessively. high value that the compressor 26 will operate to maintain the lower coil temperature.

In certain cases where the evaporator II is being used for dehumidification, the temperature of the air may fall to an undesirable value and in that case the coil I2 is used for reheating the air passing over the evaporator coil. The flow of a heating fluid such as steam through the coil I2 may be controlled by a valve 95, the valve stem 96 oi. which is connected by means of a link 91 to' the operating arm 98 of a motor 99. This motor may be a proportioning, motor of the type illustrated in Patent 2,028,110 issued to D. G. Taylor on January 14, 1936. The operation of this motor may be controlled by a thermostat I66 located in the space being conditioned. This thermostat is shown to comprise a bimetallic element |6| carrying an arm I62 for movement over resistance I63 in response to variations in temperature in the space I6. Conductors I64, I66, and I65 connect the motor 99 to the ends of resistance I63 and the bimetallic element |6| of the thermostat respectively. When the temperature in the space is at or above the desired value the arm I62 will be at the extreme right end of the resistance I63 and the motor 99 will'hold the valve 95 in closed position. Should the temperature of the air in the space drop below the desired value, the arm I02 will start to move towards the left over the resistance I03 and cause motor 99 to operate and open the valve 95 an amount which is proportional to the drop in temperature as will be understood upon reference to the above mentioned Taylor patent. In this way sufficient heat will be supplied by the coil I2 to prevent the temperature in the space I6 from dropping below the desired value.

Referring now to Figure 2 an air conditioning system similar to Figure l is illustrated. compressor motor 2| in this case however is controlled solely by the suction pressure controllers 29 and 30 toat all times maintain a certain suction pressure in the refrigeration system. I The operating circuit for the motor 2| is as follows: from the line 16 through conductors I III, mercury switch 40, conductors III, II2, mercury switch 45, conductor II3, motor 2 I, and conductor II4 to the line wire I5. It will thus be seen that the motor 2| will be operated at all times to maintain a suction pressure at least as low as the setting of the suction pressure controller 29 which may be, for example, 40 pounds.

Interposed between the condenser 23 and the expansion valve 25 is a second valve I which, may be operated by a solenoid I2I. Energlzation of the solenoid I2I causes the valve I29 to move to open position and, upon deenergization of the solenoid the valve moves to closed position either by gravity or by means of a suitabte biasing means, not illustrated. This valve remains closed as long as the temperature in he space I6 has not risen to an undes rable value so that no refrigerant is circulated through the evaporator coil II but a predetermined suction pressure is maintained in the refrigerationlsys tem. Upon an initial rise in temperature to a predetermined value the contacts 56 and 58 of the switch 54 will be bridged by the mercury element 59 as in Figure 1, thus energizing the solenoid I2! through the followin circuit: from the line 76 through conductors I25. I26. contacts 55 and 58. conductor I21. solenoid HI, and conductor I28 to the line wire I5. The energization of the solenoid I2I causes the opening of va ve I 20 whereupon refrigerant fiows through the evaporator II under the control of the expansion valve and the compressor motor 2| operates the compressor to maintain a suction pressure as con-' trolled by the controller 29 and accordingly maintains a predetermined evaporator temperature.

if now the temperature ris s to a still'h gher value so that all the contacts of the mercury switch 54 are bridged motor 24 will be energized through the following circuit which is independent of the switch 49 as follows: from the l ne wire I6 through conductors, I25. I26. contacts 56, 51. conductors I 30. I3I, 2, switch 45. conductor II3, motor 2|, and conductor H4 to the line w re I5. The compressor 20 w ll now operate to maintain a lower suction pressure and therefore a lower evaporator temperature in the evaporator coil II as in Figure 1.

Should now the humidity rise high enough so that switch 66 is tilted in theopposite direction Theits lower coil temperature in the same wayas in Figure 1. M

Upon the temperature in the space dropping to the predetermined value the valve I20 will be closed thus preventing further flow of refrigerant to the .evaporator II and the compressor motor 2| will be controlled by the suction pressure controller 29 to maintain the higher suction pressure. In this manner the suction pressure will always be maintained as low as the setting i of the controller 29 and accordingly upon a call -midity of the space areeifectively controlled, the

evaporator temperature being controlled in accordance with the need for a large or a small amount of sensible cooling and also in accordance with requirements for removal of latent heat from the air.

Having described preferred forms of my invention, many modifications may become apparent to those skilled [in the art 'and I wish it to be understood that my invention is limited only by the scope of the appended claims.

I claim as my invention:

1. In a system of the class described, refrigerating apparatus including a compressor and an evaporator, a first suction pressure controller, a second suction pressure controller, means responsive to a first condition of the air being cooled by the evaporator for placing the compressor under the control of the first suction pressure controller, and means responsive to a second condition of the air being cooled by the'evaporator for placing the compressor under the control of the second suction pressure controller.

2. In a system of the class described, refrigerating apparatus including a compressor and an evaporator, a plurality of control circuits for said compressor, one of said circuits interrupting the operation of the compressor when the pressure on the suction side of the compressor drops to a predetermined value, the other of said circuits interrupting the operation of the compressor when the pressure on the s'fiction side of the compressor ,drops to a lower predetermined value, and condition responsive means for selectively placing the compressor under the control of one or the other of said control circuits. 1

3. In a system of the class described, refrigerating apparatus including a compressor and an evaporator, means responsive to the attainment of a predetermined temperature of the air being 'cooled by the evaporator for initiatingoperation of the compressor, means responsive to the attainment of a low pressure onv the suction side of the compressor for interrupting operation thereof, and means responsive to the attainment of a still higher predetermined temperature of the air being cooled by the evaporator for lowering the suction pressure at which interruption of the compressor operation takes place.

4. In a system of the class described, refrigerating apparatus including a compressor and an evaporator, means responsive to the attainment of a predetermined temperature of the air being cooled by the evaporator for initiating operation of the compressor, means responsive to the attainment of a low pressure on the suction side of the compressor for interrupting operation thereof, and means responsive to the attainment of a predetermined high humidity of the air being cooled by the evaporator for lowering the suction pressure at which interruption oi thecompressor operation takes place.

- 5. In a system of the class described, refrigerating apparatus including a compressor and an.

evaporator, means responsive to the attainment of a predetermined temperature of the air being cooled by the evaporator for initiating operation 01' the compressor, means responsive to a condition indicative of a low evaporator temperature for interrupting operation of the compressor, means responsive to the attainment of a still higher predetermined temperature of the air being cooled by the evaporator, and means under the control of said last named means for causing operation of the compressor until the attainment of a condition indicative of a lower evaporator temperature.

6. -In a system of the class described, refrigeratingapparatus including a compressor and an evaporator, m'eans responsive to the attainment of a predetermined temperature of the air being cooled by the evaporator for initiating operation of the compressor, means responsive to a condition indicative of a low evaporator temperature for interrupting operation of the compressor,

means responsive to the attainment of'a high predetermined humidity of the air'being cooled by the evaporator, and means under the control of said last named means for causing operation of the compressor until the attainment of a condition indicative of a lower evaporator temperature.

7. An air conditioning system including a rei'rigerating apparatus having a compressor and an evaporator, means for circulating airover the ,evaporator and through a space being conditioned, means responsive to the attainment of a high predetermined temperature in the space being conditioned for initiating operation of the compressor, a pair of devices responsive to difierent pressures on the suction side of the compressor in series with said temperature responsive means for terminating operation of the compressor when the suction pressure drops to the setting of the device responsive to the highest suction pressure, and means responsive to the attainment of a higher predetermined temperature in the space for shuntingout said last named device. 8. An air conditioning system including a' refrigerating apparatus having acompressor and an evaporator, means for circulating air over the evaporator and through a space being conditioned, means responsive to the attainment 01. a high predetermined temperature in the space being conditioned for initiating operation of the compressor, a pair of devices responsive to different pressures on the suction side of the com-.

pressor in series with said temperature responsive means for terminating operation of the compressor when the suction pressure drops to the setting oi the device responsive to the highest suction pressure, and means responsive to the attainment 01' a high predetermined humidity in the space for shunting out said last named device.

9. In a system of the class described refrigcondition indicative of different evaporator temperatures selectively controlling the operation or the compressor, the device responsive to. a condition indicative of the higher evaporator temperature being normally in-control of said compressor, a valve for controlling the flow of refrigerant into the evaporator, means responsive to the attainment of a high predetermined temperature of the air being cooled by the evaporator'ior opening said valve, and means responsive to the attainment of a still higheri predetermined temperature of the air being cooled by the evaporator for placing the compressor under the control of the device responsive to a condition indicative of the lower evaporator temperature.

10. In a system of the class described, refrigerating apparatus including a compressor and an evaporator, a pair of devices responsive to a condition indicative of different evaporator temperatures selectively controlling the operation of the compressor, the device responsive to a condition indicative of the higher evaporator temperature being normally in control of said compressor, a'valve for controlling the flow of refrigerant into the evaporator, means responsive to the attainment of a high predetermined temperature of the air being cooled by the evaporator for opening said valve, and means. responsive to the attainment of a high humidity of the air being cooled by the evaporator for placing the compressor under the control of the device responsive to a condition indicative of the lower.

evaporator temperature,

11. In an air ,conditioningsystem, refrigerating apparatus including a compressor and an evaporator, means for circulating air over the evaporator and through a space to be conditioned, means for controlling the operation of the compressor including a pair of serially arranged circuit controlling devices which open in response to the attainment 01' different predetermined pressures on the suctionside of the compressor, valve merns controlling the flow oi, refrigerant into the evaporator, means respon-,

si've to the attainment of a high predetermined temperature in the space being conditioned foropen ng said valve means, and means responsive to the attainment of a still higher predeterminedv temperature in the space being conditioned for shunting out the circuit controlling device which .opens in response to the attainment of the higher pressure on the suction side of the compressor.

12. In an air conditioning system, refrigerating apparatus including acompressor and an evaporator, means for circulating air over the .sponse to the attainment'of diflerent predetermined pressures on the suction side 01 the compressor, valve means controlling the flow of refrigerant into theevaporator, means responsive to the attainment of a high predetermined temperature in the space being conditioned for opening said valve means, and means responsive to the attainment of a predetermined high humidity in the space being conditioned for shunting out the circuit controlling device which .opens in response to the attainment of the higher sure on the. suction side of the evaporator.

- WILLIAM L. McGRATH.

pres- 

